XeLabs/asm_book
2
0
Fork 0
mirror of https://github.com/pkivolowitz/asm_book.git synced 2026-06-23 15:36:45 +08:00
Code Issues Projects Releases Packages Wiki Activity

detailed example of using argv

Browse source
This commit is contained in:
Perry Kivolowitz 2023-04-13 13:38:59 -05:00
parent 6ba7a1c60d
commit 84938166f3
3 changed files with 268 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

1
README.md
View file

@ -324,6 +324,7 @@ contained therein are applicable to all languages.
| 6 | [Calling Assembly Language From Python](./python/) | [Link](./python/README.pdf) | | 6 | [Calling Assembly Language From Python](./python/) | [Link](./python/README.pdf) |
| 7 | [Atomic Operations](./more/atomics/README.md) | [Link](./more/atomics/README.pdf) | | 7 | [Atomic Operations](./more/atomics/README.md) | [Link](./more/atomics/README.pdf) |
| 8 | [Jump Tables](./more/jump_tables/README.md) | [Link](./more/jump_tables/README.pdf) | | 8 | [Jump Tables](./more/jump_tables/README.md) | [Link](./more/jump_tables/README.pdf) |
| 9 | [argv](./more/argv_example/jess1.S) | ASM CODE |
| - | [Debugging Lecture](./debugging/Discourses%20and%20Dialogs%20on%20Debugging.pptx) | PPTX | | - | [Debugging Lecture](./debugging/Discourses%20and%20Dialogs%20on%20Debugging.pptx) | PPTX |
## Macro Suite ## Macro Suite

156
more/argv_example/apple-linux-convergence.S Normal file
View file

@ -0,0 +1,156 @@
/* Macros to permit the "same" assembly language to build on ARM64
Linux systems as well as Apple Silicon systems.
See the fuller documentation at:
https://github.com/pkivolowitz/asm_book/blob/main/macros/README.md
Perry Kivolowitz
A Gentle Introduction to Assembly Language
*/
.macro GLD_PTR xreg, label
#if defined(__APPLE__)
adrp \xreg, _\label@GOTPAGE
ldr \xreg, [\xreg, _\label@GOTPAGEOFF]
#else
ldr \xreg, =\label
ldr \xreg, [\xreg]
#endif
.endm
.macro GLD_ADDR xreg, label // Get a global address
#if defined(__APPLE__)
adrp \xreg, _\label@GOTPAGE
add \xreg, \xreg, _\label@GOTPAGEOFF
#else
ldr \xreg, =\label
#endif
.endm
.macro LLD_ADDR xreg, label
#if defined(__APPLE__)
adrp \xreg, \label@PAGE
add \xreg, \xreg, \label@PAGEOFF
#else
ldr \xreg, =\label
#endif
.endm
.macro LLD_DBL xreg, dreg, label
#if defined(__APPLE__)
adrp \xreg, \label@PAGE
add \xreg, \xreg, \label@PAGEOFF
ldur \dreg, [\xreg]
// fmov \dreg, \xreg
#else
ldr \xreg, =\label
ldur \dreg, [\xreg]
#endif
.endm
.macro LLD_FLT xreg, sreg, label
#if defined(__APPLE__)
adrp \xreg, \label@PAGE
add \xreg, \xreg, \label@PAGEOFF
ldur \sreg, [\xreg]
#else
ldr \xreg, =\label
ldur \sreg, [\xreg]
#endif
.endm
.macro GLABEL label
#if defined(__APPLE__)
.global _\label
#else
.global \label
#endif
.endm
.macro MAIN
#if defined(__APPLE__)
_main:
#else
main:
#endif
.endm
/* Fetching the address of the externally defined errno is quite
different on Apple and Linux. This macro leaves the address of
errno in x0.
*/
.macro ERRNO_ADDR
#if defined(__APPLE__)
bl ___error
#else
bl __errno_location
#endif
.endm
.macro CRT label
#if defined(__APPLE__)
bl _\label
#else
bl \label
#endif
.endm
.macro START_PROC // after starting label
.cfi_startproc
.endm
.macro END_PROC // after the return
.cfi_endproc
.endm
.macro PUSH_P a, b
stp \a, \b, [sp, -16]!
.endm
.macro PUSH_R a
str \a, [sp, -16]!
.endm
.macro POP_P a, b
ldp \a, \b, [sp], 16
.endm
.macro POP_R a
ldr \a, [sp], 16
.endm
/* The smaller of src_a and src_b is put into dest. A cmp instruction
or other instruction that sets the flags must be performed first.
This macro makes it easy to remember which register does what in the
csel.
Thank you to u/TNorthover for nudge to add the cmp.
*/
.macro MIN src_a, src_b, dest
cmp \src_a, \src_b
csel \dest, \src_a, \src_b, LT
.endm
/* The larger of src_a and src_b is put into dest. A cmp instruction
or other instruction that sets the flags must be performed first.
This macro makes it easy to remember which register does what in the
csel.
Thank you to u/TNorthover for nudge to add the cmp.
*/
.macro MAX src_a, src_b, dest
cmp \src_a, \src_b
csel \dest, \src_a, \src_b, GT
.endm
.macro AASCIZ label, string
.p2align 2
\label: .asciz "\string"
.endm
.macro MOD src_a, src_b, dest, scratch
sdiv \scratch, \src_a, \src_b
msub \dest, \scratch, \src_b, \src_a
.endm

111
more/argv_example/jess1.S Normal file
View file

@ -0,0 +1,111 @@
#include "apple-linux-convergence.S"
.p2align 2
.text
GLABEL main
/* This program will get a string followed by a double followed by an
integer from the command line demonstrating how each of these types
can be retrieved.
Example:
./a.out test 29.3 29
*/
MAIN
PUSH_P x29, x30
mov x29, sp
// Check argc to see if it is 4. This is not the only way to
// validate command line arguments but it is an easy way.
cmp w0, 4
bne 99f // take branch if argc isn't "right".
// Skip past argv[0]
add x1, x1, 8
// Fetch argv[1] as a string.
// x1 is a pointer to a pointer to chars (i.e. the string).
// Being a pointer to a pointer, it must be dereferenced to
// make a pointer.
ldr x0, [x1] // dereference
// Now x0 contains a pointer to the command line argument.
// Print the string (as a string). But doing this causes a
// function call which will destroy x1. So, save x1 temporarily.
// This could be avoided if x1 were moved to a backed up x
// register (e.g. x20).
PUSH_R x1
CRT puts // ptr is in x0 where puts() needs it.
POP_R x1
// Advance x1 once again to get to argv[2] which can be done
// in the same instruction as dereferencing it use a
// preincrement.
ldr x0, [x1, 8]! // dereference
// Now the string version of argv[2] is now pointed to by x0.
// This is exactly where atof would want it. We need atof
// because it turns strings into numbers. BUT, same as before,
// calling a function would destroy x1 so let's do the same
// trick of backing up x1 on the stack and then restoring after
// the function call.
PUSH_R x1
CRT atof // ptr is in x0 where atof() needs it.
POP_R x1
// The string value will be converted to a double left in d0.
// d0 is also a scratch register so for our next call to atoi,
// d0 will have to be preserved on the stack - alternatively,
// we could have used a high d register backed up and restored
// at the start and ending of main().
// Advance x1 once again to get to argv[3] which can be done
// in the same instruction as dereferencing it use a
// preincrement.
ldr x0, [x1, 8]! // dereference
// Now the string version of argv[3] is now pointed to by x0.
// This is exactly where atoi would want it. We need atoi
// because it turns strings into numbers. BUT, same as before,
// calling a function would destroy x1 so let's do the same
// trick of backing up x1 on the stack and then restoring after
// the function call. We must also do the same for d0. Actually,
// we won't need argv after this so we will skip backing up x1.
PUSH_R d0
CRT atoi // ptr is in x0 where atof() needs it.
POP_R d0
// d0 now contains the double.
// x0 now contains the integer.
// x0 must be copied to x1 because x0 must be a pointer to fmt
// for printf to work.
mov x1, x0
LLD_ADDR x0, fmt
#if defined(__APPLE__)
sub sp, sp, 16
str x1, [sp, 8]
str d0, [sp]
CRT printf
add sp, sp, 16
#else
bl printf
#endif
99: POP_P x29, x30
mov w0, wzr
ret
/* What did we learn?
* x1 has argv when main begins.
* pointers to the arguments are the contents of argv NOT
the actual values. Therefore, x1, which is a pointer (to a pointer),
must be dereferenced to get to the actual pointer. In the code,
there are three lines with the comment "// dereference".
* all command line arguments are c-strings. If that's not what you
want, they must be converted - see the code for atoi and atof for
examples.
*/
.data
fmt: .asciz "double: %f integer: %d\n"
.end